Possible treatment options for the Control of Oryctes rhinoceros, the coconut rhinoceros beetle (CRB), developed by the Coconut Rhinoceros Beetle Response on Oʻahu, Hawaiʻi
Background
The coconut rhinoceros beetle (CRB) is an invasive large black beetle from Southeast Asia. CRB is becoming widespread on Oahu and is a serious pest of palms. CRB prefer coconut, phoenix, royal, and fan including Pritchardia (loulu) palms but can feed on other palm types. They less frequently feed on hala (pandanus, or screwpine), sugarcane, and pineapple. Damage to palms results in slower growth, lower yield, unsightly frond damage and if CRB populations are high, the damage will kill palms. We recommend removal of dead palms but we do not generally recommend removal of living palms. CRB do not inhabit the palms long-term so reducing palm numbers will concentrate the damage on existing palms or drive CRB to new areas.
There is no single treatment currently available to completely rid an area of CRB but there are several treatments and practices that can reduce the impacts of CRB. These practices are most effective when combined. If CRB are found on your property or you have CRB damage on palms, we recommend:
Removal of all potential breeding material (mulch, compost, rich soil, stumps, dead trees, plant waste piles). Treatment is needed before removal if the material is infested.
Avoid accumulation or bringing in new potential breeding material.
Treatment of host palms (systemic pesticides; imidacloprid, acephate and/or netting in crowns of short trees).
Sanitation
CRB breed in decaying plant material (not just palm). Mulch and compost are ideal habitat for breeding but stumps, leaves, lawn thatch, and rich soil are also breeding material. CRB can also breed in leaf/frond debris in palms and rotting areas of the crown and trunk. Cleaning the debris from the upper crown near the spear can reduce the chance of breeding in trees. Reducing the amount of these materials in your location limits the amount of breeding material and suppresses populations. Removal and incineration of all green waste at Mamala Bay Golf Course, the first breeding site for CRB found on Oahu, has led to >95% reduction in CRB since the first detection there in 2013.
Infested material can be treated to kill CRB. There are several methods that will kill 100% of CRB in the infested material. Only incineration prevents reinfestation and material treated by other methods should be removed to a hot composting facility, secured in a CRB-proof container, or re-treated every 4 months. Decaying plant material should not be transported without treatment. Businesses and individuals must have a compliance agreement with HDOA if they move loads larger than 3 cubic yards.
Best treatments
Incineration: Incineration kills all CRB and there is no material left to reinfest. Burning requires permits from the Dept. of Health so is not possible in all cases. Material can be sent to H-POWER but they charge tipping fees and they have limits on green waste so scheduling is required.
Heat treatment: Any heat treatment that brings all the material to >131 degrees F (55 C) will kill CRB. Common methods include hot composting in wind rows and in-vessel composting. Steam heat treatment is possible but less common.
Fumigation: Treatment with sulfuryl fluoride (e.g. Profume or Vikane) to 2000 CT will kill all life stages of CRB. This can be done in a vault or tarped similar to home treatments for termites. This treatment requires a certified pesticide applicator with a category 7 certification.
Chipping: Chipping infested material will kill CRB. This is only practical for whole unchipped material like branches, palm fronds, or logs.
Intermediate treatments
Grinding: Grinding will kill some CRB but kill rates have not been tested. Finer (smaller particle size) grinding is more likely to kill more CRB.
Submersion: Submerging breeding material in water will drown larvae but adults will be able to escape. Submersion for 24 hours will kill many larvae but 48 hours or more is preferable.
Manual search: digging through the material and observing every inch of it will allow you to pull out many CRB present. This is unreasonable for larger piles and eggs and small larvae are easy to miss.
Minimal treatment
Spread thin: Spreading mulch and compost thinner than 2 inches dries out the material faster and allows predators (chickens and mongoose) to find CRB. If material stays moist or is irrigated this is not a treatment for CRB.
Till in: Tilling material into soil reduces the scent, access, and calories per volume available to CRB. The smaller the organic component of the soil is, the lower the attractiveness will be to CRB.
Palm Treatments
CRB adults visit trees for feeding but do not typically stay in trees very long. A CRB may feed on different trees throughout their life. Treatments to trees include pesticides and physical barriers. Pesticides are applied as foliar sprays, systemic injections, or systemic root drench. Physical barriers include netting and sand. Physical treatments can protect a single palm but pesticides should be applied to all palms in an area to be effective. Since systemic pesticides require CRB to feed on the palm to die, damage will still occur but will be reduced when there is a reduction in the local CRB population. Transport of palms on Oahu requires a compliance agreement with HDOA whether they are treated or not.
Chemical
Injection: Imidacloprid (e.g. ImaJet) and Acephate (e.g. AceJet) kill CRB in lab trials and have reduced populations when applied to most palms in an area. Systemic injections require trimming of flowers and fruits at least every 6 months to protect pollinators and ensure the fruits are not consumed.
Soil drench: Imidacloprid (e.g. Imidacloprid 75 WSP) can be applied as a soil drench for systemic treatment of palms. Field efficacy has not been tested for this application method. Soil drench with imidacloprid requires trimming of flowers and fruits at least every 6 months to protect pollinators and ensure the fruits are not consumed. Fully trimmed palms can be treated as “shrubs” when consulting the label for application instructions.
Foliar spray: Spraying of the crown with cypermethrin (e.g. Demon Max) has been shown to kill CRB in the lab and field. However, this treatment is currently only approved for experimental use. Spraying the spear and upper central part of the crown will be more effective than spraying outer and lower frond areas.
Physical
Netting: Netting can entangle and exclude CRB from accessing the crown of the tree. Netting should be one inch stretched hole size to three inch stretched hole size and wrapped around the base of the spear in 2 or more layers and stuffed between the bases of fronds near the spear.
Sand: Sand can be applied to the crown so that it sits between the bases of the fronds surrounding the spear. The efficacy of this treatment has not been tested. Sand requires regular reapplication as it washes away and new fronds grow out from the spear.
Organic mulch alternatives
There are several alternatives to mulch for water retention and weed control that don't put host palms at increased risk of CRB attack. Inorganic soil coverings will reduce the soil surface evaporation rate and temperature and will last much longer than mulch. Water permeable weed mat, landscaping rock, gravel, rubber chips/pellets, and recycled asphalt gravel are a few common choices. For water retention, products that are incorporated beneath the soil surface work best. Water retention crystals hold much more water than mulch and are not very expensive.
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